1. Field of the Invention
The present invention relates to a wideband phase shift device more particularly a phase shift device for a receiver used in the framework of digital terrestrial television, such as an OFDM (pour Orthogonal Frequency Division Multiplexing) receiver.
2. Description of the Prior Art
In a standard signal reception system for DVB-T (Digital Video Broadcasting-Terrestrial) digital terrestrial television, a modulation of the OFDM type is most frequently used. This is a particularly robust modulation and makes the isofrequency retransmission of a DVB-T channel possible in a domestic environment. The DVB-T signals can thus be captured at a point in the environment where they are at a sufficient level, then amplified and retransmitted in the environment to be captured identically from this retransmitter by “portable” digital receivers such as digital television sets or analogue television sets equipped with digital terrestrial decoders. This is the principle retained for Digital Terrestrial Television (DTT).
Nevertheless, in spite of the robustness of the modulation, notable reception problems occur for portable reception.
Currently, the solution favoured for obtaining a more robust reception consists in the use of more than one antenna (typically 2).
The two antennas are therefore physically positioned so as to receive two decorrelated received signals corresponding to the same transmitted signal. The distance for allowing the signals at the two antenna accesses to be decorrelated being approximately equal to 0.7 times the wavelength of the received signal, a difference between antennas in the order of 45 cm is obtained for the UHF band (470-860 MHz). It thus appears unrealistic to consider this type of relatively cumbersome concept owing to the dimension of the radiating elements.
Another technique consists in implementing a smart antenna device constituted by at least two separate RF (Radio frequency) accesses with a wideband phase shifter that can be controlled on one of the channels and a combination of the received signals, as shown in FIG. 1a. 
However, the implementation of these two techniques is not easy, in the frequency band considered, owing to the congestion of the function at the relatively low frequencies considered here [470-860 MHz] as they do not enable an octave to be covered. Moreover, they cannot be integrated into a single component.
Another integrable approach consists of generating two quadrature signals (sine and cosine) from a single signal. Such an integrable circuit is shown in FIG. 1b. Each of these signals thus drives a variable gain amplifier LNA1 and LNA2, voltage controlled by a bias circuit CP. The particularity of this bias circuit is that the resultant at the output is amplitude constant, the phase of the resulting signal at the output varying according to the control voltage. However this integrable technique in a component does not enable an octave to be covered either.
The invention aims to overcome these disadvantages.